A conventional vehicular audio-amplifier controller includes a control circuit such as a digital signal processor (DSP) or a central processing unit (CPU) and is supplied with sound signals from various input sources. The control circuit outputs a sound signal to an audio amplifier. The audio amplifier amplifies the sound signal and outputs a sound via a speaker installed in a vehicle (e.g., see patent literature 1).
It is favorable to decrease power consumption of a vehicular power supply in a vehicle (particularly a hybrid car or an electric car) as much as possible. The power efficiency can be increased by decreasing a power-supply voltage of the vehicular power supply as much as possible.
For example, control over detecting an input signal and changing a power-supply voltage of the audio amplifier may use a technology that changes the power-supply voltage in anticipation of a margin voltage as security against a sudden change in the input signal. This type of technology can compute a tendency of input signals and use a result for control processing so as to minimize the margin and improve the efficiency, but leaves room for improvement of the power efficiency.